An important and difficult challenge in biotechnology is unleashing the vast potential of carbon capture in cellulosic materials for conversion into valuable substances such as liquid fuel, chemicals, food, and other products. One specific challenge relates to using xylose, commonly found in depolymerized hemicellulose, as a carbon source for the heterotrophic cultivation of microorganisms. Although much work has been done in using xylose in the production of ethanol using yeast, most yeast strains either cannot utilize xylose or utilize xylose only very inefficiently (see Jeffries, 2006, Curr. Op. Biotech. 17: 320-326; and Wang et al., 2004, Biotechnol. Lett. 26(11): 885-890).
Certain oleaginous microorganisms (e.g. oleaginous yeast and oleaginous microalgae) are capable of converting fixed-carbon energy sources into higher value products such as triglycerides, fatty acids, carbohydrates, and proteins. In addition, the microalgae themselves can be valuable as a food source. For example, certain species of oleaginous microalgae have been genetically engineered to produce “tailored oils”, which means that their triglyceride content shows altered distributions of fatty acid chain lengths and saturation relative to the strains from which they were derived. See PCT Pub. Nos. 2008/151149, 2009/126843, 2010/045358, 2010/063031 and 2010/063032 and PCT App. Nos. U.S. Ser. No. 11/038,463 and U.S. Ser. No. 11/038,464.
The ability to convert xylose to lipid and other products in meaningful amounts using oleaginous microorganisms would be of major environmental significance because it would reduce our dependence on fossil fuels and reduce the cost of microbial oils.